The central hypotheses of Research Project II are 1) that reading and writing are complex skills that depend on a number of component processes that have both shared and independent genetic and environmental etiologies in children with disabilities, and 2) that patterns of covariation in etiology will provide unique insights into the cognitive architecture underlying these skills and into the nature of learning disabilities. Project II will assess component processes in reading, writing, and related language skills in twins and siblings selected for deficits in reading and/or ADHD, and in normal-range control twins. The broad age range of the sample allows us to assess developmental differences in skills and in the expression of disabilities across grades 2-12. Our long-running assessment of word recognition, orthographic coding, phonological decoding, and phonological awareness will be continued to support more powerful and informative behavioral and molecular genetic analyses of these skills, but our main emphasis will be on the relations of these skills to reading fluency, reading and listening comprehension, writing, and higher-level language skills. Univariate multiple regression (DF) analyses will be used to evaluate the genetic and environmental etiologies for deficits in each skill. Bivariate DF analyses and confirmatory factor analyses of twin data will be used to assess the genetic and environmental covariance among the different skills. Behavior-genetic analyses will also be used to validate subtypes and/or dimensions of individual differences among children with reading and writing disabilities by assessing their differential genetic and environmental etiology. In collaboration with Research Projects I, III, and IV, QTL analyses will be used to assess genetic linkage and association for deficits in different reading, writing, and language skills. In collaboration with Research Project III, we will explore the relations of these deficits to different symptoms and cognitive components of ADHD. In collaboration with Project V, we will explore the effects of intense computerassisted intervention in 2nd to 4th grade twins'homes for the remediation of deficits in these skills. New and recently introduced measures included in Project II will allow the first thorough analysis of genetic and environmental influences on component processes in reading fluency, reading comprehension, listening comprehension, and writing.